The present invention relates to a toner for developing an electrostatic image in an image forming method such as electrophotography, electrostatic recording or electrostatic printing and, more particularly, to a dry toner for use in an image forming apparatus, such as a copying machine, a laser printer or a facsimile machine.
A developer for use in electrophotography, electrostatic recording, electrostatic printing and so on is once adhered to an image carrier such as a photoconductor on which an electrostatic latent image has been formed in a developing process. The toner image thus obtained is then transferred from the photoconductor to a transfer medium such as a transfer paper in a transfer process, and fixed on the paper in a fixing process. As a developer for developing the electrostatic image formed on a latent image holding surface of the image carrier, a two-component developer composed of a carrier and a toner and a one-component developer requiring no carrier (magnetic or nonmagnetic toner) are known.
Dry toners for use in electrophotography, electrostatic recording, electrostatic printing and so on, have been hitherto produced by melt-kneading a toner binder such as a styrene resin or a polyester together with a colorant and so on, the resulting kneaded mixture being subsequently dried and finely pulverized.
The known dry toners have one or more of the following problems.
After having been developed and transferred to a paper or the like, such a dry toner is heat-melted and fixed with a heat roll. At this time, when the temperature of the heat roll is excessively high, the toner is excessively melted and adhered to the heat roll (hot offset). When the temperature of the heat roll is excessively low, on the other hand, the toner is not sufficiently melted, resulting in insufficient fixation. With a view to energy saving and downsizing of an apparatus such as a copying machine, a toner which does not cause hot offset at a high fixing temperature (namely, has hot offset resistance) and which can be fixed at a low fixing temperature (namely, has low-temperature fixation efficiency) is demanded. The toner should also have heat-resistant preservability so as not to cause blocking during storage or under ambient temperature in an apparatus in which the toner is used. Especially, a toner for use in a full-color copying machine and a full-color printer need to have a low melt viscosity to provide gloss and color mixability in a printed-image, so that a polyester type toner binder having a sharp melt property is used therein. Since such a toner is likely to cause hot offset, a silicone oil or the like is conventionally applied to a heat roll in full-color machines. However, in order to apply a silicone oil to a heat roll, an oil tank and an oil applying unit are necessary, which makes the apparatus unavoidably complicated and large. Also, application of oil causes deterioration of the heat roll, so that the heat roll requires regular maintenance. Additionally, it is unavoidable for the oil to adhere a copying paper and an OHP (overhead projector) film. Especially, the oil adhered to OHP film impairs color tone of a printed image.
For the purpose of producing an image with high fineness and high quality, improved toners having a small particle size have been proposed. However, particles of a toner produced by a normal kneading-pulverizing method have irregular shapes. As a consequence, when, in the case of being used as a two-component developer, the toner is agitated with a carrier in a developing unit or when, in the case of being used as a one-component developer, the toner particles receive a contact stress from a developing roller, a toner supply roller, a layer thickness regulating blade, a frictional electrification blade and so on, the toner particles are apt to be further pulverized to generate superfine particles and, additionally, a fluidizing agent such as an external additive is apt to be buried in the surface of the toner particles, resulting in deterioration of image quality. Also, the toner is poor in fluidity as a powder because of the irregular shapes of the particles thereof, and thus requires a large amount of fluidizing agent or cannot be filled in a toner bottle with a high filling rate, which hinders downsizing of the apparatus.
Additionally, a process of transferring an image formed of color toners to produce a full-color image from a photoconductor to a transfer medium or a paper is becoming more complicated, so that low transferability of a pulverized toner due to the irregular shapes of the particles thereof causes a void in a transfer image and an increase in consumption of toners to prevent it.
Thus, there is an increasing demand for reducing toner consumption without causing a void in a transferred image by improving transfer efficiency and for decreasing running cost. When transfer efficiency is significantly high, there is no need for a cleaning unit for removing untransferred toner from a photoconductor and a transfer medium, which leads to downsizing of the apparatus and cost reduction in manufacturing the same. This has also a merit of generating no waste toner. For the purpose of overcoming the drawbacks of the toner of irregular particle shape, there have been proposed various methods for producing spherical toner particles.
For the purpose of providing a toner having heat-resistant preservability, low-temperature fixation efficiency and hot offset resistance, there have been proposed (1) a toner in which a polyester partially crosslinked using a multifunctional monomer is used as a toner binder (Japanese Laid Open Patent Publication No. S57-109825) and (2) a toner in which a urethane-modified polyester is used as a toner binder (Japanese Examined Patent Publication No. H07-101318). For the purpose of providing a toner for use in a full-color system which can reduce the amount of oil to be applied to the heat roll, (3) a toner produced by granulating polyester fine particles and wax fine particles is proposed (Japanese Laid-Open Patent Publication No. H07-56390). Proposed for the purpose of providing a toner having improved powder fluidity and transferability when its particle size is reduced are (4) a polymerized toner obtained by dispersing a vinyl monomer composition containing a colorant, a polar resin and a releasing agent in water and suspension-polymerizing the vinyl monomer composition (Japanese Laid Open Patent Publication No. H09-43909) and (5) a toner obtained by sphering toner particles comprising a polyester type resin in water using a solvent (Japanese Laid Open Patent Publication No. H09-34167). Additionally, Japanese Laid-Open Patent Publication No. H11-133666 discloses (6) a dry toner consisting of nearly spherical particles in which a polyester modified with a urea bond is used as a bonder.
However, none of the toners (1) to (3) have sufficient powder fluidity and transferability and thus can produce a high-quality image even when its particle size is reduced. The toners (1) and (2) cannot compatibly satisfy the heat-resistant preservability and the low-temperature fixation efficiency and do not develop sufficient gloss to be used in a full color system. The toner (3) is insufficient in the low-temperature fixation efficiency and the hot offset resistance in oilless fixation. The toners (4) and (5) are improved in the powder fluidity and the transferability. However, the toner (4) is insufficient in the low-temperature fixation efficiency and requires much energy to fix. This problem is pronounced when the toner is used in full-color printing. The toner (5), which is superior to the toner (4) in the low-temperature fixation efficiency, is insufficient in hot offset resistance and thus cannot preclude the necessity of the application of oil to the heat roll in a full-color system.
The toner (6) is excellent in that the viscoelasticity of the toner can be appropriately adjusted by using a polyester extended by a urea bond and that it can compatibly satisfy both good gloss and good releasing property as a full-color toner. Especially, a phenomenon called xe2x80x9celectrostatic offsetxe2x80x9d in which unfixed toner on a transfer medium is scattered or adhered to a fixing roller due to electrification of the fixing roller during use can be reduced by neutralization of positive charges of the urea bond component with weak negative charges of the polyester resin. However, it has been found that the toner (6) still has problems in practice with respect to service life. Namely, when, in the case of being used as a two-component developer, the toner is agitated with a carrier in a developing unit or when, in the case of being used as a one-component developer, the toner particles receive a contact stress from a developing roller, a toner supply roller, a layer thickness regulating blade, a frictional electrification blade and so on, the toner particles are apt to be further pulverized to generate superfine particles and, additionally, a fluidizing agent such as an external additive is apt to be buried in the surface of the toner particles, resulting in deterioration of image quality.
It is, therefore, an object of the present invention to provide a dry toner which is excellent in powder fluidity and transferability when its particle size is reduced, in heat-resistant preservability, in developing efficiency, in image quality, in low-temperature fixation efficiency, in service life and in offset resistance.
Another object of the present invention is to provide a dry toner which can produce high gloss and high quality in a printed image when used in a full-color copying machine or the like.
As a result of earnest studies for solving the above problems, the present inventors have made the present invention.
In accordance with the present invention, there is provided a dry toner for developing an electrostatic image, comprising a toner binder comprising a modified polyester, said toner having a volume average particle diameter Dv of 3 to 10 xcexcm and such a number average particle diameter Dp that the ratio Dv/Dp of the volume average particle diameter to the number average particle diameter ranges from 1.05 to 1.25.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments of the invention to follow.
A dry toner according to the present invention comprises a toner binder including a modified polyester. It is important that the toner have a volume average particle diameter Dv of 3 to 10 xcexcm and such a number average particle diameter Dp that the ratio Dv/Dp of the volume average particle diameter to the number average particle diameter ranges from 1.05 to 1.25.
The dry toner according to the present invention exhibits excellent heat-resistant preservability, low-temperature fixation efficiency and offset resistance. When used in a full-color copying machine, the dry toner can produce high gloss and high quality images. When used in the form of a two-component developer, the toner shows only a small variation in particle size throughout a long period of service with occasional replenishment thereof. Thus, the toner can withstand a long period of use and agitation and can shows high developing efficiency in a stable manner for a long time. Also, when used in the form of a single-component developer, the toner shows only a small variation in particle size and does not cause toner filming on a developing roller, a regulating blade or the like member which is brought into frictional contact with the toner throughout a long period of service with occasional toner replenishment. Thus, the toner can withstand a long period of use and agitation and can shows high developing efficiency in a stable manner for a long time.
The constitutional features of the dry toner of the present invention will be described in more detail below.
Particle Size:
The dry toner has a volume average particle diameter Dv of 3 to 10 xcexcm and a number average particle diameter Dp providing a ratio Dv/Dp of the volume average particle diameter to the number average particle diameter in the range from 1.05 to 1.25. When the volume average particle diameter Dv is less than 3 xcexcm, the toner is apt to be fused and to deposit on carrier particles during a long period of use in the case of a two-component developer. Such deposits adversely affect the charging characteristics of the carrier. In the case of a single-component developer, the toner having a volume average particle diameter Dv of less than 3 xcexcm is apt to cause formation of toner filming on a developing roller, a regulating blade or the like member during a long period of service.
When the volume average particle diameter Dv is greater than 10 m, it is difficult to obtain toner images having high resolution and high quality. Additionally, the toner shows a significant variation in particle size during a long period of service with occasional replenishment thereof. These disadvantages are also caused when the ratio Dv/Dp of the volume average particle diameter to the number average particle diameter is greater than 1.25. When the Dv/Dp is less than 1.05, on the other hand, it becomes difficult to sufficiently charge the toner. In addition, cleaning of a surface of a latent image bearable member such as a photoconductor for the removal of the toner remaining thereon is not easy.
Modified Polyester:
The modified polyester as used herein is intended to refer to a polyester to which one or more groups or polymer components (other than ester groups and those originally contained in the alcohol or carboxylic acid monomer units of the polyester) are bonded (through ionic bonding or covalent bonding) or added.
Examples of such modified polyesters include a modified polyester obtained by reacting the terminal group or groups thereof with a group other than an ester group such as an isocyanate group. The isocyanate-modified terminal may further be reacted with an active hydrogen-containing compound, which may be, if desired, further subjected to a chain extending reaction.
Another example of the modified polyester is one which is obtained linking termini of polyester molecules with a compound having a plurality of active hydrogen-containing groups. Illustrative of such modified polyesters are urea-modified polyester and urethane-modified polyester.
A further example of the modified polyester is one which is obtained by introducing a reactive group or groups containing one or more double bonds into the main polyester skeleton. The reactive group or groups are subjected to radical polymerization so that graft chain or chains are introduced. Alternatively, the reactive group or groups are subjected to crosslinking so that the polyester molecules are crosslinked together. Illustrative of such modified polyesters are styrene-modified polyester and acrylic-modified polyester.
A further example of the modified polyester is one which is obtained by introducing (for example, by copolymerization) a polymer, such as a silicone resin whose terminus or termini are modified with a carboxyl group, a hydroxyl group, an epoxy group or a mercapto group, into the carboxyl or hydroxyl terminus of the polyester or the main skeleton of the polyester. One specific example of such a modified polyester is a silicone-modified polyester.
A urea-modified polyester is preferably used as the modified polyester. The urea-modified polyester may be suitably prepared by reacting an isocyanate-containting polyester prepolymer with an amine. The isocyanate-containting polyester prepolymer may be obtained by reacting a polyisocyanate with a polyester which is prepared by polycondensation of a polyol with a polyacid and which has an active hydrogen. Examples of active hydrogen-containing groups include a hydroxyl group (alcoholic OH or phenolic OH), an amino group, a carboxyl group and a mercapto group.
The polyol may be a diol or a tri- or more polyhydric alcohol. A mixture of a diol with a minor amount of a tri- or more polyhydric alcohol is preferably used.
As the diol to be used for the preparation of the base polyester, any diol employed conventionally for the preparation of polyester resins can be employed. Preferred examples include alkylene glycols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 2,3-butanediol, diethylene glycol, triethylene glycol, dipropylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol and 2-ethyl-1,3-hexanediol; alkyleneether glycols such as diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol and polytetramethylene ether glycol; alicyclic glycols such as 1,4-cyclohexane dimethanol and hydrogenated bisphenol A; bisphenols such as bisphenol A, bisphenol F and bisphenol S; alkylene oxide adducts (e.g. ethylene oxide, propylene oxide and butylene oxide adducts) of the above alicyclic diols; and alkylene oxide adducts (e.g. ethylene oxide, propylene oxide and butylene oxide adducts) of the above bisphenols. Above all, alkylene glycols having 2 to 12 carbon atoms and alkylene oxide adducts of bisphenols are preferred. Especially preferred is the use of a mixture of alkylene glycols having 2 to 12 carbon atoms with alkylene oxide adducts of bisphenols.
Examples of the polyol having three or more hydroxyl groups include polyhydric aliphatic alcohols such as glycerin, 2-methylpropane triol, trimethylolpropane, trimethylolethane, pentaerythritol, sorbitol and sorbitan; phenol compounds having 3 or more hydroxyl groups such as trisphenol PA, phenol novolak and cresol novolak; and alkylene oxide adducts of the phenol compounds having 3 or more hydroxyl groups.
The polyacid may be a dicarboxylic acid, tri- or more polybasic carboxylic acid or a mixture thereof.
As the dicarboxylic acid to be used for the preparation of the base polyester, any dicarboxylic acid conventionally used for the preparation of a polyester resin can be employed. Preferred examples include alkyldicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid and sebacic acid; alkenylene dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid and itaconic acid; and aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid and naphthalene dicarboxylic acid. Above all, alkenylene dicarboxylic acids having 4 to 20 carbon atoms and aromatic dicarboxylic acids having 8 to 20 carbon atoms are preferably used.
Examples of tri- or more polybasic carboxylic acids include aromatic polybasic carboxylic acids having 9 to 20 carbon atoms such as trimellitic acid and pyromellitic acid.
The polyacids may be in the form of anhydrides or low alkyl esters (e.g. methyl esters, ethyl esters and isopropyl esters).
In the formation of the polyester, the polyacids and the polyols are used in such a proportion that the ratio [OH]/[COOH] of the equivalent of the hydroxyl groups [OH] to the equivalent of the carboxyl groups [COOH] is in the range of generally 2:1 to 1:1, preferably 1.5:1 to 1:1, more preferably 1.3:1 to 1.02:1.
Examples of the polyisocyanate compound reacted with the polyester include aliphatic polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate and 2,6-diisocyanate methylcaproate; alicyclic polyisocyanates such as isophorone diisocyanate, cyclohexylmethane diisocyanate; aromatic diisocyanate such as xylylene dilsocyanate, tolylene diisocyanate, diphenylmethane diisocyanate and xcex1,xcex1,xcex1xe2x80x2,xcex1xe2x80x2-tetramethylxylylene diisocyanate; isocyanurates; the above polyisocyanates blocked or protected with phenol derivatives, oximes or caprolactams; and mixtures thereof.
The polyisocyanate is used in such an amount that the ratio [NCO]/[OH] of the equivalent of the isocyanate groups [NCO] to the equivalent of the hydroxyl groups [OH] of the polyester is in the range of generally 5:1 to 1:1, preferably 4:1 to 1.2:1, more preferably 2.5:1 to 1.5:1. A [NCO]/[OH] ratio of over 5:1 tends to adversely affect low-temperature fixation efficiency of the resulting toner. Too small a [NCO]/[OH] ratio of less than 1 tends to adversely affect anti-hot offset properties of the resulting toner.
The isocyanate group-containing polyester prepolymer generally has a content of the polyisocyate unit in the range of 0.5 to 40% by weight, preferably 1 to 30% by weight, more preferably 2 to 20% by weight. Too small an isocyanate group content of less than 0.5% tends to adversely affect anti-hot offset properties and to pose a difficulty in simultaneously obtaining satisfactory low-temperature fixation efficiency and heat-resisting preservability of the resulting toner. When the isocyanate group:content exceeds 40% by weight, the low-temperature fixation efficiency of the resulting toner tends to be adversely affected.
The average number of the isocyanate groups contained in the prepolymer molecule is generally at least 1, preferably 1.5 to 3, more preferably 1.8 to 2.5. Too small a isocyanate group number less than 1 will result in a urea-modified polyester having an excessively small molecular weight so that the anti-hot offset properties of the toner will be adversely affected.
Examples of the amine to be reacted with the isocyanate group-containing polyester prepolymer for the formation of the urea-modified polyester include diamines, polyamines having 3 or more amino groups, aminoalcohols, aminomercaptans, amino acids and blocked or protected derivatives thereof.
Illustrative of suitable diamine""s are aromatic diamines such as phenylenediamine, diethytoluenediamine and 4,4xe2x80x2-diaminodiphenylmethane; alicyclic diamines such as 4,4xe2x80x2-diamino-3,3-dimethylcyclohexylmethane, diaminocyclohexane and isophoronediamine; and aliphatic diamines such as ethylenediamine, tetramethylenediamine and hexamethylenediamine. Illustrative of suitable polyamines having 3 or more amino groups are diethylenetriamine and triethylenetetramine. Illustrative of suitable aminoalcohols are ethanolamine and hydroxyethylaniline. Illustrative of suitable aminomercaptans are aminoethylmercaptan and aminopropylmercaptan. Illustrative of suitable amino acids are aminopropionic acid and aminocaproic acid. Illustrative of suitable blocked derivatives of the above diamines, polyamines having 3 or more amino groups, aminoalcohols, aminomercaptans and amino acids are ketimines obtained by interacting the amines with a ketone such as acetone, methyl ethyl ketone or methyl isobutyl ketone. Oxazolidine compounds may be also used as the blocked derivatives. Especially preferred amine is an aromatic diamine or a mixture of an aromatic diamine with a minor amount of a polyamine having 3 or more amino groups.
If desired, a chain extension terminator may be used to control the molecular weight of the urea-modified polyester. Examples of the chain extension terminators include monoamines such as diethylamine, dibutylamine, butylamine and laurylamine. Blocked or protected monomines such as ketimines may be also used as the terminator.
The amine is reacted with the isocyanate group-containing polyester prepolymer in such an amount that the ratio [NCO]/[NHx] of the equivalent of the isocyanate groups [NCO] of the prepolymer to the equivalent of the amino groups [NHx] of the amine is in the range of generally 1:2 to 2:1, preferably 1.5:1 to 1:1.5, more preferably 1.2:1 to 1:1.2. A [NCO]/[NHx] ratio over 2:1 or less than 1:2 will result in a urea-modified polyester having an excessively small molecular weight so that the anti-hot offset properties of the toner will be adversely affected.
One specific example of a method of producing the urea-modified polyester is as follows. A polyol and a polyacid are reacted with each other in the presence of an esterification catalyst such as tetrabutoxytitanate or dibutyltin oxide at a temperature of 150 to 280xc2x0 C. The reaction may be carried out under a reduced pressure while removing water produced in situ, if desired. The resulting hydroxyl group-containing polyester is reacted with a polyisocyanate at 40 to 140xc2x0 C. in the presence or absence of a solvent to obtain an isocyanate-containing prepolymer. The prepolymer is reacted with an amine at 0 to 140xc2x0 C. in the presence or absence of a solvent to obtain a urea-modified polyester. Any solvent inert to the polyisocyanate may be used. Examples of the solvents include aromatic solvents such as toluene and xylene; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; esters such as ethyl acetate; amides such. as dimethylformamide and dimethylacetamide; and ethers such as tetrahydrofuran.
The urea-modified polyester may contain an urethane linkage, if desired. The content of the urethane linkage is generally up to 90 mole %, preferably up to 80 mole %, more preferably up to 70 mole %, based on total of the urethane and urea linkages. Too large an amount of the urethane linkage above 90 mole % may adversely affect the anti-hot offset properties of toner.
The modified polyester used in the present invention may be prepared by one-shot method or a prepolymer method. The modified polyester generally has a weight average molecular weight of at least 10,000 preferably 20,000 to 107, more preferably 30,000 to 106. Too small a weight average molecular weight of less than 10,000 may adversely affect the anti-hot offset properties of toner. When the modified polyester is used by itself as the binder, the number average molecular weight thereof is generally 20,000 or less, preferably 1000 to 10,000, more preferably 2,000 to 8,000. Too large a number average molecular weight above 20,000 may adversely affect low-temperature fixation efficiency of the resulting toner and gloss of color toner images. When the modified polyester is used in conjunction with an unmodified polyester as the toner binder, however, the number average molecular weight thereof is not specifically limited but may be arbitrarily determined in view of the above weight average molecular weight.
Unmodified Polyester:
It is preferred that the modified polyester be used in conjunction with an unmodified polyester as the toner binder for reasons of improved low-temperature fixation efficiency of the toner and improved gloss of the toner images. The unmodified polyester may be polycondensation products obtained from polyols and polyacids. Suitable polyols and polyacids are as described previously with reference to the modified polyester. For reasons of improved low-temperature fixation efficiency, it is preferred that the modified polyester and the unmodified polyester be compatible at least in part with each other. The amount of the unmodified polyester in the toner binder is such that the weight ratio of the modified polyester to the unmodified polyester is generally 5:95 to 80:20, preferably 5:95 to 30:70, more preferably 5:95 to 25:75, most preferably 7:93 to 20:80. Too small an amount of the modified polyester below 5% by weight is disadvantageous because the anti-hot offset properties are deteriorated and because it is difficult to attain both heat resistive preservability and low-temperature fixation efficiency simultaneously.
The unmodified polyester generally has a peak molecular weight of 1,000 to 30,000, preferably 1,500 to 10,000, more preferably 2,000 to 8,000, for reasons of ensuring satisfactory heat-resistant preservability and low-temperature fixation efficiency. The term xe2x80x9cpeak molecular weightxe2x80x9d as used herein is intended to refer to the molecular weight at which the main peak is present in the molecular weight distribution thereof when measured by gel permeation chromatography.
Toner Binder:
The toner binder used in the present invention generally has a glass transition point of 40 to 70xc2x0 C., preferably 55 to 65xc2x0 C. A glass transition point of less than 40xc2x0 C. tends to cause deterioration of heat resistive preservability, while too high a glass transition point of over 70xc2x0 C. tends to cause deterioration of low-temperature fixation efficiency. Because of the presence of the modified polyester, the dry toner of the present invention exhibits superior heat resistance and preservability even thought the glass transition point of the toner is low.
The toner binder preferably has such a storage elasticity that the temperature (TGxe2x80x2) at which the storage elasticity is 10,000 dyne/cm2 at a measurement frequency of 20 Hz is at least 100xc2x0 C., preferably 110 to 200xc2x0 C., for reasons of resistance to hot offset.
The toner binder also preferably has such a viscosity that the temperature (Txcex7) at which the viscosity is 1,000 poise at a measurement frequency of 20 Hz is 180xc2x0 C. or less, preferably 90 to 160xc2x0 C., for reasons of low-temperature fixation efficiency.
Preferably, TGxe2x80x2 is higher than Txcex7 from the standpoint of attainment of both low-temperature fixation efficiency and resistance to hot offset. In other words, it is preferred that the difference (TGxe2x80x2xe2x88x92Txcex7) is 0xc2x0 C. or greater, more preferably at least 10xc2x0 C., most preferably at least 20xc2x0 C. The upper limit is not specifically defined. From the standpoint of attainment of both low-temperature fixation efficiency and heat resistant preservability, the difference (Txcex7xe2x88x92Tg) is 0 to 10xc2x0 C., more preferably 10 to 90xc2x0 C., most preferably 20 to 80xc2x0 C.
The toner binder generally has a hydroxyl value of at least 5, preferably 10 to 120, more preferably 20 to 80. Too low a hydroxyl value of less than 5 is disadvantageous to simultaneously attain both good heat resistive preservability and low-temperature fixation efficiency of the toner. The toner binder generally has an acid value of 1 to 30 mg KOH, preferably 5 to 20 mg KOH for reasons of improved compatibility between the toner and paper and improved fixing efficiency.
Colorant:
As the colorant usable for the electrostatic image developing toner of the present invention, any colorant known to be used conventionally for the preparation of a toner can be employed. Suitable colorants for use in the toner of the present invention include known pigments and dyes. These pigments and dyes can be used alone or in combination.
Specific examples of such dyes and pigments include carbon black, Nigrosine dyes, iron black, Naphthol Yellow S, Hansa Yellow (10G, 5G and G), cadmium yellow, yellow colored iron oxide, loess, chrome yellow, Titan Yellow, polyazo yellow, Oil Yellow, Hansa Yellow (GR, A, RN and R), Pigment Yellow L, Benzidine Yellow (G and GR), Permanent Yellow NCG)-, Vulcan Fast Yellow (5G and R), Tartrazine Yellow Lake, Quinoline Yellow Lake, Anthracene Yellow BGL, isoindolinone yellow, red iron oxide, red lead, orange lead, cadmium red, cadmium mercury red, antimony orange, Permanet Red 4R, Para Red, Fire Red, p-chloro-o-nitro aniline red, Lithol Fast Scarlet G. Brilliant Fast Scarlet, Brilliant Carmine BS, Permanent Red (F2R, F4R, FRL, FRLL and F4RH), Fast Scarlet VD, Vulkan Fast Rubine B, Brilliant Scarlet G, Lithol Rubine GX Permanent F5R, Brilliant Carmine 6B, Pigment Scarlet 3B, Bordeaux 5B, Toluidine Maroon, Permanent Bordeaux F2K, Helio Bordeaux BL, Bordeaux 10B, BON Maroon Light, BON Maroon Medium, Eosine Lake, Rhodamine Lake B, Rhodamine Lake Y, Alizarine Lake, Thioindigo red B, Thioindigo Maroon, Oil Red, quinacridone red, Pyrazolone Red, polyazo red, Chrome Vermilion, Benzidine Orange, perynone orange, Oil Orange, cobalt blue, cerulean blue, Alkali Blue Lake, Peacock Blue Lake, Victoria Blue lake, metal-free Phthalocyanine Blue, Phthalocyanine Blue, Fast Sky Blue, Indanthrene Blue (RS, BC), indigo, ultramarine, prussian blue, Anthraquinone Blue, Fast Violet B, Methyl Violet Lake, cobalt violet, manganese violet, dioxane violet, Anthraquinone Violet, Chrome Green, zinc green, chromium oxide, viridian, emerald green, Pigment Green B, Naphthol Green B, Green Gold, Acid Green Lake, Malachite Green Lake, Phthalocyanine Green, Anthraquinone Green, titanium oxide, zinc oxide, lithopone, and the like. These dyes and pigments are employed alone or in combination. The content of a coloring agent in the toner of the present invention is preferably from about 1 to 15% by weight, more preferably 3-10% by weight, based on the weight of the toner.
In one embodiment of the production of toner, the colorant is composited with a resin binder to form a master batch.
As the binder resin for forming the master batch, the above-described modified polyester, unmodified polyester may be used. Further, various other polymers may also be used for the formation of the master batch. Specific examples of such other polymers for use in the formation of the master batch include homopolymers of styrene or substituted styrenes such as polystyrene, polychlorostyrene, and polyvinyltoluene; styrene-based copolymers such as styrene-p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-methyl xcex1-chloromethacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinylethyl ether copolymer, styrene-vinylmethylketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, and styrene-maleic acid ester copolymer; and polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyvinylbutyl butyral, polyacrylic resin, rosin, modified rosin, terpene resin, phenolic resin, aliphatic hydrocarbon resin, alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, and paraffin wax. These polymers can be used alone or in combination.
The master batch may be obtained by mixing and kneading the binder resin and the colorant while applying a large shear strength thereto using a suitable kneader such as a three-roller mill. In this case, an organic solvent may be used to enhance the interaction between the resin and the colorant. If desired, xe2x80x9cflushingxe2x80x9d method may be adopted to obtain the master batch. In this method, an aqueous paste containing a colorant is mixed and kneaded together with a binder resin and an organic solvent so that the colorant migrates to the organic phase. The organic solvent and water are then removed.
Releasing Agent:
The toner of the present invention preferably contains a wax as a releasing agent in addition to the toner binder and the colorant. The wax preferably has a melting point of 40 to 160xc2x0 C., preferably 50 to 120xc2x0 C., more preferably 60 to 90xc2x0 C. A melting point of the wax below 40xc2x0 C. may adversely affect the heat resistance and preservability of the toner, while too high a melting point in excess of 160xc2x0 C. is apt to cause cold offset of toner when the fixation is performed at a low temperature. Preferably, the wax has a melt viscosity of 5 to 1000 cps, more preferably 10 to 100 cps, at a temperature higher by 20xc2x0 C. than the melting point thereof. When the viscosity is greater than 1000 cps, the anti-hot offset properties and low fixation efficiency of the toner are adversely affected.
Any wax may be suitably used for the purpose of the present invention. Examples of such wax include polyolefin wax, such as polyethylene wax and polypropylene wax; long chain hydrocarbon wax, such as paraffin wax and sazole wax; and carbonyl group-containing wax.
The carbonyl group-containing wax is preferably used for the purpose of the present invention. Illustrative of suitable carbonyl group-containing waxes are polyalkanoic acid ester waxes such as carnauba wax, montan wax, trimethylolpropane tribehenate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate and 1,18-octadecanediol distearate; polyalkanol ester waxes such as tristearyl trimellitate and distearyl maleate; polyalkanoic acid amide waxes such as ethylenediamine dibehenyl amide; polyalkylamide waxes such as trimellitic acid tristearyl amide; and dialkyl ketone waxes such as distearyl ketone. Above all, the use of a polyalkanoic acid ester wax is preferred.
The amount of the wax in the toner is generally 0 to 40% by weight, preferably 3 to 30% by weight, based on the weight of the toner.
Charge Controlling Agent:
The toner of the present invention may contain a charge controlling agent, if desired. Any charge controlling agent generally used in the field of toners for use in electrophotography may be used for the purpose of the present invention. Examples of such charge controlling agents include a nigrosine dye, a triphenylmethane dye, a chromium-containing metal complex dye, a molybdic acid chelate pigment, a rhodamine dye, an alkoxyamine, a quaternary ammonium salt including a fluorine-modified quaternary ammonium salt, alkylamide, phosphorus and a phosphorus-containing compound, tungsten and a tungsten-containing compound, a fluorine-containing activator material, and metallic salts of salicylic acid and derivatives thereof.
Specific examples of the charge controlling agents include Bontron 03 (Nigrosine dyes), Bontron P-51 (Quaternary ammonium salts), Bontron S-34 (metal-containing azo dyes), E-82 (oxynaphthoic acid type metal complex), E-84 (salicylic acid type metal complex) and E-89 (phenol type condensation products), which are manufactured by Orient Chemical Industries Co., Ltd.; TP-302 and TP-415 (quaternary ammonium salts molybdenum complex), which are manufactured by Hodogaya Chemical Co., Ltd.; Copy Charge PSY VP2038 (quaternary ammonium salts), Copy Blue PR (triphenylmethane derivatives), Copy Charge NEG VP2036 (quaternary ammonium salts) and Copy Charge NX VP434(quaternary ammonium salts), which are manufactured by Hoechst AG; LRA-901 and LR-147 (boron complex), which are manufactured by Japan Carlit Co.; copper Phthalocyanine; perylene; quinacridone; azo type pigments; and polymer compounds having a functional group such as a sulfonic acid group, a carboxyl group or a quaternary ammonium salt group.
The amount of-charge control agent for use in the color toner may be determined in light of the kind of binder resin to be employed, the presence or absence of additives, and the preparation method of the toner including the method of dispersing the composition of the toner. It is preferable that the amount of charge control agent be in the range of 0.1 to 10 parts by weight, and more preferably in the range of 0.2 to 5 parts by weight, per 100 parts by weight of the binder resin. By the addition of the charge control agent in such an amount, sufficient chargeability for use in practice can be imparted to the toner. Further, electrostatic attraction of the toner to a developing roller can be prevented, so that the decrease of fluidity of the developer and the decrease of image density can be prevented.
The charge controlling agent and wax may be mixed and kneaded with the binder resin or the above master batch.
External Additive:
Inorganic fine particles may be suitably used, as an external additive, to improve the fluidity, developing efficiency and chargeability of the toner by being attached to outer surfaces of the toner particles. Such inorganic fine particles include silica, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, quartz sand, clay, mica, wallstonite, diatomaceous earth, chromium oxide, cerium oxide, iron oxide red, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide and silicon nitride. These inorganic fine particles preferably have a primary particle diameter of 5 mxcexc (5 nm) to 2 xcexcm, more preferably 5 mxcexc to 500 mxcexc, and a BET specific surface area of 20 to 500 m2/g. The inorganic fine particles are used in an amount of generally 0.01 to 5% by weight, preferably 0.01 to 2% by weight, based on the weight of the toner.
The external additive (fluidizing agent) may also be fine particles of a polymeric substance such as polystyrene, polymethacrylate or an acrylate copolymer obtained by soap-free emulsion polymerization, suspension polymerization or dispersion polymerization; silicone, benzoguanamine or nylon obtained by polycondensation; or a thermosetting resin.
By subjecting these fluidizing agents to a surface treatment to improve the hydrophobic properties thereof, deterioration of the fluidity and the charge properties of the toner can be avoided even under high humidity conditions. Suitable surface treating agents include silane coupling agents, silane coupling agents having a fluorinated alkyl group, organic titanate type coupling agents, aluminum type coupling agents, silicone oil and modified silicone oil.
Cleaning property improving agents may be also used in the toner of the present invention for facilitating the removal of toner remaining on a photoconductor or an intermediate transfer medium after the transference. Examples of such cleaning property improving agents include fatty acids and their metal salts such as stearic acid, zinc stearate and calcium stearate, and particulate polymers such as polymethyl methacrylate particles and polystyrene particles which are manufactured, for example, by the soap-free emulsion polymerization method. The particulate polymer preferably has a volume average particle diameter of 0.01 to 1 xcexcm.
Description will now be made of a method of preparing the dry toner according to the present invention.
Kneading and Pulverizing Method:
First, ingredients of the toner such as a binder including a modified polyester resin, a coloring agent, wax and a charge controlling agent are mechanically mixed with each other using a mixer such as a rotary blade mixer to obtain a mixture.
The mixture is then kneaded using a suitable kneader. A single axis type (or single cylinder type) kneader, a two axis type (or two cylinder type) continuous extruder; or a roll mill may be suitably used as the kneader. The kneading should be performed at a temperature near the softening point of the binder resin so as not to cause breakage of the molecular chain of the binder resin. Too high a temperature above the softening point will cause breakage of the molecular chain of the binder resin. The dispersion of the coloring agent, etc. in the binder resin will not sufficiently proceed when the temperature is excessively lower than the softening point.
The kneaded mixture is then solidified and the solidified mixture is grounded, preferably in two, coarsely grinding and succeeding finely grinding stages. The earlier stage may be carried out by impinging the solidified mixture to an impact plate under a jet stream, while the later stage may be performed using a combination of a rotor and a stator with a small gap. The ground mixture is classified in a jet flow utilizing tangential force to obtain a toner having an average size of, for example, 5 to 20 xcexcm.
The thus obtained toner is, if desired, mixed with an external additive such as a fluidizing agent to improve the fluidity, preservability, developing efficiency and transfer efficiency. The mixing with the external additive may be carried out using a conventional mixer preferably capable of controlling the mixing temperature. The external additive may be added gradually or at once. The rotational speed, mixing time and mixing temperature may be varied in any suitable manner. Illustrative of suitable mixers are v-type mixers, rocking mixers, Ledige mixers, nauter mixers and Henschel mixers.
As methods to obtain spherical toner, there may be mentioned a mechanical method in which ingredients of the toner such as a binder and a colorant are melt-kneaded, solidified, ground and further processed with a hybridizer or a mechanofusion; a spray dry method in which ingredients of the toner are dispersed in a solution of a toner binder dissolved in a solvent, the dispersion being subsequently spray dried; and a dispersion method in which spherical toner particles are produced in an aqueous medium. The dispersion method is preferably used for the purpose of the present invention. This method is described in more detail below.
Toner Preparation by Dispersion in Aqueous Medium:
In the dispersion method, an organic solvent solution or dispersion containing ingredients of the toner such as a binder resin or a prepolymer thereof and wax is dispersed in an aqueous medium with stirring, preferably while applying heat and shear forces to the wax, to form toner particles which are subsequently separated and dried.
In one method, a dry toner may be obtained by a method in which a toner composition containing a modified polyester is dissolved or dispersed in an organic solvent to prepare a liquid. This liquid is then dispersed in an aqueous medium to obtain a dispersion containing particles of the toner composition. Spherical toner is obtained by removing the solvent from the particles.
Alternatively, a dry toner may be obtained by a method in which a prepolymer composition containing a prepolymer is dissolved or dispersed in an organic solvent to prepare a liquid. The liquid is dispersed in an aqueous medium to obtain a dispersion. The dispersion is then subjected to a polyaddition reaction to polymerize the prepolymer and to obtain a reaction mixture containing dispersed therein particles of a toner composition comprising the modified polyester obtained from the prepolymer. Spherical toner is obtained by removing the solvent from the particles.
The aqueous medium used in the dispersion method may be water by itself or a mixture of water with a water-miscible solvent such as an alcohol, e.g. methanol, isopropanol or ethylene glycol; dimethylformamide; tetrahydrofuran; cellosolve, e.g. methyl cellosolve; or a lower ketone, e.g. acetone or methyl ethyl ketone.
The modified polyester used in the dispersion method may be a prepolymer thereof. The prepolymer may be converted into the modified polyester during the dispersing step in the aqueous medium by reaction with, for example, a chain extender or a crosslinking agent. For example, a urea-modified polyester may be produced during the dispersing step in the aqueous medium by reaction of an isocyanate-containing polyester prepolymer with an amine. The reaction may be performed at a temperature of 0 to 150xc2x0 C. (under a pressurized condition), preferably 40 to 98xc2x0 C., for 10 minutes to 40 hours, preferably 2 to 24 hours in the presence of, if desired, a catalyst such as dibutyltin laurate or dioctyltin laurate.
The formation of the urea-modified polyester from its prepolymer by reaction with an amine may be carried out either before or after dispersing the prepolymer-containing composition in an aqueous medium. When the reaction with the amine is performed after the prepolymer-containing composition has been dispersed in the aqueous medium, the amine is reacted with the prepolymer on surfaces of the particles.
It is preferred that other ingredients, such as a colorant, a colorant master batch, a wax, a charge controlling agent and an unmodified polyester, than the modified polyester be previously mixed with the modified polyester (or a prepolymer thereof) in an organic solvent. However, at least one of such ingredients may be added to the aqueous medium at the time of dispersing the organic solvent solution of the modified polyester (or a prepolymer thereof) into the aqueous medium or after the formation of toner particles dispersed in the aqueous medium, if desired. For example, the colorant may be incorporated into the toner after the toner particles containing the wax, the binder, etc. have been prepared.
Dispersion into the aqueous phase may be carried out using any desired dispersing device, such as a low speed shearing type dispersing device, a high speed shearing type dispersing device, an abrasion type dispersing device, a high pressure jet type dispersing device or an ultrasonic-type dispersing device. A high speed shearing type dispersing device is preferably used for reasons of obtaining dispersed toner particles having a diameter of 2 to 20 xcexcm in a facilitated manner. The high speed shearing type dispersing device is generally operated at a revolution speed of 1,000 to 30,000 rpm, preferably 5,000 to 20,000 rpm. The dispersing time is generally 0.1 to 5 minutes in the case of a batch type dispersing device. The dispersing step is generally performed at 0 to 150xc2x0 C. (under a pressurized condition), preferably 40 to 98xc2x0 C. A higher temperature is suitably used to decrease the viscosity of the mass.
The aqueous medium is generally used in an amount of 50 to 2,000 parts by weight, preferably 100 to 1,000 parts by weight per 100 parts by weight of the toner composition containing the modified polyester (or a prepolymer thereof) and other ingredients for reasons of obtaining suitable dispersion state.
A dispersing agent may be used in dispersing the toner composition into the aqueous medium to stabilize the dispersion and to obtain sharp particle size distribution. Examples of the dispersing agent include anionic surface active agents such as a salt of alkylbenzensulfonic acid, a salt of xcex1-olefinsulfonic acid and a phosphoric ester; cationic surface active agents such as amine surfactants (e.g. an alkylamine salt, an aminoalcohol fatty acid derivative, a polyamine fatty acid derivative and imidazoline), and quaternary ammonium salt surfactants (alkyl trimethylammonium salt, dialkyl dimethylammonium salt, alkyl dimethylammonium salt, pyridium salt, alkyl isoquinolinium salt and benzethonium chloride; nonthe modified polyester (or a prepolymer thereof) the modified polyester (or a prepolymer thereof); nonionic surface active agent such as a fatty amide derivative and polyhydric alcohol derivative; and ampholytic surface active agents such as alanine, dodecyl di(aminoethyl)glycine and di(octylaminoethyl)glycine and N-alkyl-N,N-dimethylammoniumbetaine.
A surfactant having a fluoroalkyl group can exert its effects in an only very small amount and is preferably used.
Suitable anionic surfactants having a fluoroalkyl group include fluoroalkylcarboxylic acids having 2 to 10 carbon atoms and their metal salts, perfluorooctanesulfonylglutamic acid disodium salt, 3-[omega-fluoroalkyl(C6-C11)oxy]-1-alkyl(C3-C4)sulfonic acid sodium salts, 3-[omega-fluoroalkanoyl (C6-C8)-N-ethylamino]-1-propanesulfonic acid sodium salts, fluoroalkyl (C11-C20)carboxylic acids and their metal salts, perfluoroalkyl(C7-C13)carboxylic acids and their metal salts, perfluoroalkyl(C4-C12)sulfonic acid and their metal salts, perfluorooctanesulfonic acid diethanolamide, N-propyl-N-(2-hydroxyethyl)perfluorooctanesulfonamide, perfluoroalkyl(C6-C10)sulfoneamidopropyl trimethylammonium salts, perfluoroalkyl (C6-C10)-N-ethylsulfonylglycine salts, and monoperfluoroalkyl(C6-C16)ethylphosphoric acid esters.
Examples of tradenames of anionic surfactants having a perfluoroalkyl group include Surflon S-111, S-112 and S-113 (manufactured by Asahi Glass Co., Ltd.), Florard FC-93, Ec95, FC-98 and FC-129 (manufactured by Sumitomo 3M Ltd.), Unidine DS-101 and DS-102 (manufactured by Daikin Co., Ltd.), Megafac F-111, F-120, F-113, F-191, F-812 and F-833 (manufactured by Dainippon Ink and Chemicals, Inc.), Ektop EF-102, 103, 104, 105, 112, 123A, 123B, 306A, 501, 201 and 204 (manufactured by Tochem Products Co., Ltd.), and Phthargent F-100 and F-150 (manufactured by Neos co., Ltd.).
Examples of suitable cationic surfactants having a fluoroalkyl group include primary, secondary or tertiary aliphatic amine salts; aliphatic quaternary ammonium salts such as perfluoroalkyl(C6-C10) sulfonamidopropyltrimethyl-ammonium salts; benzalkonium salts; benzethonium chloride; pyridinium salts; and imidazolinium salts. Tradenamed cationic surfactants include Surflon S-121 (Asahi Glass Co., Ltd.), Florard FC-135 (manufactured by Sumitomo 3M Ltd.), Unidine DS-202 (manufactured by Daikin Co.), Megafac F-150 and F-824 (Dainippon Ink and Chemicals Inc.), Ektop EF-132 (manufactured by Tochem Products Co., Ltd.), and Phthargent F-300 (manufactured by Neos Co., Ltd.).
In addition, dispersants of inorganic compounds, which are hardly soluble in water, such as tricalcium phosphate, calcium carbonate, titanium oxide, colloidal silica, and hydroxyapatite can also be employed.
In addition, dispersed particles can be stabilized with polymer type protective colloids. Specific examples of such polymer type protective colloids include homopolymers and copolymers of the following compounds:
acids such as acrylic acid, methacrylic acid, xcex1-cyanoacrylic acid, xcex1-cyanomethacrylic acid, itaconic acid, crotonic acid, fumaric acid, maleic acid, and maleic anhydride;
(meth)acrylic monomers such as xcex2-hydroxyethyl acrylate, xcex2-hydroxyethyl methacrylate, xcex2-hydroxypropyl acrylate, xcex2-hydroxypropyl methacrylate, xcex3-hydroxypropyl acrylate, xcex3-hydroxypropyl methacrylate, 3-chloro-2-hydroxypropyl acrylate, 3-chloro-2-hydroxypropyl methacrylate, diethylene glycol monoacrylic acid esters, diethylene glycol monomethacrylic acid esters, glycerin monoacrylic acid esters, glycerin monomethacrylic acid esters, N-methylol acrylamide, and N-methylol methacrylamide;
vinyl alcohol, ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl propyl ether;
esters of vinyl alcohol with a carboxylic acid such as vinylacetate, vinylpropionate and vinyl butyrate; amides such as acrylamide, methacrylamide, diacetoneacrylamide, and their methylol compounds;
acid chloride compounds such as acrylic acid chloride, and methacrylic acid chloride;
homopolymers and copolymers of compounds having a nitrogen atom or a heterocyclic ring including a nitrogen atom such as vinyl pyridine, vinyl pyrrolidone, vinyl imidazole and ethylene imine;
polyoxyethylene compounds such as polyoxyethylene, polyoxypropylene, polyoxyethylenealkylamine, polyoxypropylenealkylamine, polyoxyethylene-alkylamide, polyoxypropylenealkylamide, polyoxyethylene-nonylphenylether, polyoxyethylene-laurylphenylether, polyoxyethylenestearylphenylether, and polyoxyethylene-nonylphenylether; and
cellulose compounds-such as methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.
For the purpose of reducing the viscosity of the prepoiymer-containing composition or the modified polyester resin-containing composition in the dispersion, an organic solvent capable of dissolving the prepolymer or the modified polyester resin may be used. As the organic solvents, there may be mentioned aromatic hydrocarbons such as toluene, xylene and benzene; halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, 1,2-dichloroethane, 1,1,2-trichloroethane, trichloroethylene, chloroform, monochlorobenzene and dichlorloethylidene; esters such as methyl acetate and ethyl acetate; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. These solvents may be used singly or in combination. The amount of the organic solvent is generally 0 to 300 parts by weight, preferably 0 to 100 parts by weight, more preferably 25 to 70 parts by weight, per 100 parts by weight of the modified polyester (or a prepolymer thereof). The use of the solvent can produce toner particles having a narrow particle size distribution.
The dispersion or emulsion of toner particles in the aqueous medium thus prepared is then treated to remove the organic solvent. The removal of the organic solvent can be carried out by gradually heating the dispersion to evaporate the organic solvent and also water to dryness. Alternatively, the dispersion is sprayed into a dry atmosphere to evaporate the organic solvent to obtain fine toner particles which are then dried to remove water. The dry atmosphere may be a gas, such as air, nitrogen, carbon dioxide, combustion gas, which is heated above the boiling point of the organic solvent used. A spray drier, a belt drier or a rotary kiln may be used for separating and drying the toner particles.
When a dispersing agent capable of being dissolved in an acid or an alkali is used, washing with an acid or alkali and then with water can remove the dispersing agent from the toner particles. For example, calcium phosphate may be removed by washing with an acid and then with water. An enzyme may be also used to remove certain kinds of the dispersing agent. Although the dispersing agent can be retained on the toner particles, the removal thereof is preferable for reasons of charging characteristics of the toner.
It is preferred that the dispersion or emulsion of toner particles in the aqueous medium prepared above be heat treated at a temperature of at least about 50xc2x0 C. but not higher than the melting point of the releasing agent (wax) to reduce the irregular size toner particles. The heat treatment is preferably carried out after the removal of the organic solvent but may be conducted before the solvent removing step, if desired. The heat treatment temperature is preferably higher than the softening point of the modified polyester.
When the toner particles in the dispersion obtained have a wide particle size distribution, classification may be conducted. The classification for the removal of excessively fine particles is preferably carried out before separation of the toner particles from the dispersion for reasons of efficiency, though the classification may be preceded by the separation and drying of the particles. Classification for the removal of fine particles may be performed using, for example, a cyclone, a decanter or a centrifugal device. Air classification may be suitably adopted for the removal of large particles after drying of the toner particles. Large and small particles thus separated may be reused as raw materials for the preparation of the toner.
The thus obtained toner particles can be mixed with different types of particles such as a particulate release agent, a particulate charge controlling agent, a particulate fluidizing agent and a particulate colorant. By applying mechanical force to the mixture, these different particles can be fixed and unified with the surface of the toner particles and thereby the different particles are prevented from releasing from the resultant complex particles. Methods useful for applying mechanical force include impacting the mixture rapidly-rotating blades; and discharging the mixture into a high speed airflow so that the particles of the mixture accelerate and collide with each other or the particles impact against a proper plate or some such object. Specific examples of such apparatuses include an Ong Mill (manufactured by Hosokawa Micron Co., Ltd.), modified I type Mill in which pressure of air for pulverization is reduced (manufactured by Nippon Pneumatic Co., Ltd.), Hybridization System (manufactured by Nara Machine Co., Ltd.), Kryptron System (manufactured by Kawasaki Heavy Industries, Ltd.), and automatic mortars.
The toner according to the present invention can be used as a two-component developer after mixed with a carrier or as a one-component developer or microtoning developer having magnetic powders incorporated in the toner.
When the toner of the present invention is employed as a two-component developer, any conventionally-known carrier can be used. In this case, the toner is generally used in an amount of 1 to 10 parts by weight per 100 parts by weight of the carrier. Examples of the carrier include magnetic powders such as iron powders, ferrite powders, magnetite powders, magnetic resin powders and nickel powders and glass beads, and these powders having a surface treated with a resin. The magnetic toner generally has a particle diameter of 20 to 200 xcexcm. Examples of the resin for covering the surface of the carrier include amino resins, urea-formaldehyde resins, melamine resins, benzoguanamine resins, urea resins, polyamide resins and epoxy resins. Also usable for covering carrier are polyvinyl or polyvinylidene resins; polystyrene-type resins such as acrylic resins, polymethyl methacrylate resins, polyacrylonitrile resins, polyvinyl acetate resins, polyvinyl fluoride resins; polyvinyl butyral resins, polyvinyl alcohol resins, polystyrene resins and styrene-acrylic acid copolymers; halogenated olefin resins such as polyvinyl chloride resins; polyester resins such as polyethylene terephthalate resins and polybutylene terephthalate resins; polycarbonate resins; polyethylene resins; polyvinylidene fluoride resins; polytrifluoroethylene resins; polyhesafluoropropylene resins; copolymers of vinylidene fluoride and acrylic monomer; copolymers of vinylidene fluoride and vinyl fluoride; terpolymers of tetrafluoroethylene, vinylidene fluoride and a fluorine-free monomer; and silicone resins. The resin coating for the carrier may contain conductive powder such as metal powder, carbon black, titanium oxide, tin oxide or zinc oxide. The conductive powder preferably has an average particle diameter of 1 xcexcm or less for reasons of easy control of the electric resistance.
The toner of the present invention may be used as a one-component magnetic or nonmagnetic toner requiring no carrier.
The following examples will further illustrate the present invention. Parts are by weight. The particle diameter (volume average particle diameter and number average particle diameter) is measured using Coulter counter TA-II or Coulter Multisizer II (manufactured by Coulter Electronics Inc.).